Tap changing system



Oct. 2, 1934. w Q SEALEY 1 975 176 TAP CHANGING.SYSTEM Filed Jan. 11, 1933 Patented Oct. 2, 1934 UNITED STATES PATENT ()FFI'CE TAP CHANGING SYSTEM Application January 11, 1933, Serial No. 651,171

11 Claims.

This invention relates in general to a system for changing the taps on transformers, reactors, and other inductive apparatus, and more particularly to such a system in which a plurality of I independent preventive coils are employed to reduce the flow of circulating current when adjacent taps are bridged by the tap switch mechanism.

The utility of this invention is best understood by reference to the transformer art where it is customary to employ a single mid-tapped preventive coil with its ends connected to spaced contact arms which alternately bridge adjacent tap contacts and engage the same contact. In

such systems the switch mechanism is complicated and may even exceed the cost of the transformer itself.

An object of the present invention is to provide a tap changing system in which a tap switch having a single movable contact element is operable to connect one or more preventive coils in series with a tapped Winding without interrupting the circuit through said winding.

Another object of this invention is to provide a tap changing system in which a preventive coil is connected in series with each tap on a multiply tapped winding so that the coils connected with adjacent taps are in inductive opposition.

A further object of this invention is to provide a tap changing system in which a separate preventive coil is connected with each tap of a multiply tapped winding and a simple tap switch is arranged to energize certain of the coils in certain positions and to short circuit the coils in other positions.

A still further object of the invention is to pro vide a system of the above type having two serially connected sections of winding, one or both of which are tapped, and one or more cores having a plurality of separate preventive coils wound thereon in inductive opposition to each other.

These and other objects and advantages are attained by this invention, various novel features of which will be apparent from the description and drawing herein, and will be more particularly pointed out in the claims.

Various illustrative examples of the application of this invention are shown in the accompanying drawing in which:

Fig. 1 is a schematic diagram of a tap changing system embodying the present invention;

Fig. 2 is a schematic diagram of the system shown in Fig. 1, with the short circuiting feature of applicants invention added thereto; and

. Fig. 3 is a schematic diagram of a tap changing system employing two multiply tapped winding sections connected in series and embodying the present invention.

Referring now to the drawing, Figs. 1, 2 and 3 each show a transformer 10 having a Winding 11 connected across power line having conductors 12 and 13 and a winding having sections 14 and 15 which are adapted to be serially connected across a power line having conductors 16 and 17 by means of mechanism to be more fully described hereinafter. It is to be understood that either one of the power lines may be of higher potential than the other or of equal potential, or in other words, the tap mechanism may be associated with either the primary or secondary winding of the transformer.

In Fig. 1, winding section 14 is provided with a plurality of taps 21 to 25, inclusive. A preventive coil assembly 18 comprises coils 31 to 35, inclusive, wound on core 26 and connected with taps 21 to 25, inclusive, in such a manner that the coils connected to adjacent taps are in inductive opposition with respect to load current flowing therethrough. The other ends of preventive coils 31 to 35, inclusive, are respectively connected to stationary contacts 41 to 45, inclusive, of tap changing switch mechanism 28. This switch mechanism is provided with a single rotatable contact arm 46 and a slip ring or pig tail connection 47, noting that the contact portion of arm 46 is of sufficient Width to bridge adjacent stationary contacts in moving to and from the positions in which a single stationary contact is engaged. In the position shown in Fig. 1 winding sections 14 and 15 are serially connected across power line having conductors 16 and 17 through taps 24 and 25, preventive coils 34 and 35 to contacts 44 and 45 through switch arm ,46 and connection 4'7 to the upper end of winding section 15, noting that the load current in this .95 position of the switch mechanism will divide between coils 34 and 35 and that the currents through these coils will produce magneto motive forces which mutually oppose each other so that the reactive voltage drop through these preventive coils will be reduced to a minimum. It is also to be noted that circulating currents through the section of the winding between taps 24 and 25, through coils 34 and 35 and through contacts 44 and 45 will be reduced to a minimum by reason of the inductance of preventive coils 34 and 35 which are mutually additive with respect to such circulating currents. When switch arm 46 is moved so as to engage only a single stationary contact the total load current will no flow through a single preventive coil thus producing a slight voltage drop in said coil due to the impedance thereof.

Fig. 2 illustrates how the above described voltage drop in a single preventive coil may be obviated by providing the tap changing switch mechanism with an additional set of stationary contacts 51 to 55, inclusive, and an additional contact member 48 on contact arm 46. In this embodiment of the invention the preventive coils connected with adjacent taps will function in the same manner as described in connection with Fig. 1, however, when the movable contact member is moved so as to engage a single stationary contact the single preventive coil connected with the selected contact will be short circuited by the auxiliary contact 48. In this connection it is to be noted that as movable contact arm 16 moves from a bridging position, contact 48 will not engage a stationary auxiliary contact until after the bridging connection has been broken. However, in some instances it may be desirable to short circuit a preventive coil simultaneously with the breaking of the bridging connection. The switch mechanism described in connection with Figs. 1 and 2 is, for the sake of simplicity, illustratedas being. of the drum or dial type,

however, it is to be understood that the same connections may be established by means of a plurality of separate switches which are sequentially operated.

Referring now to Fig. 3, winding section 14 is provided with a plurality of taps 21, 22 and 23 and winding section 15 is provided with taps 61, 62 and 63. Various portions of each winding section are adapted to be serially connected across power line having conductors 16 and 1'7 by means of tap switch mechanism 28 through various coils of the preventive coil assembly 18. This assembly comprises two independent cores 26 and 27 upon which coils 31 to 33, inclusive, and 81 to 83, inclusive, are wound respectively, however, it is to be understood that a single core such as shown in Figs. 1 and 2 may be used. Switch mechanism 28 comprises a plurality of stationary contacts '71, 72 and '73 connected to taps 21, 22 and 23, respectively, through preventive coils 31, 32 and 33 and a plurality of stationary contacts 91, 92 and 93 which are connected to taps 61, 62, and 63, respectively, through preventive coils 81, 82 and 83. This switch mechanism also comprises a movable contact arm 95 which is adapted in certain positions to bridge two stationary adjacent contact members and in other positions to bridge three stationary adjacent contact members. In the position of contact arm 95 shown load current passes through preventive coil 31 and divides in passing through preventive coils 82 and 81 in a manner similar to that above described in connection with Figs. 1 and 2. When contact member 95 is rotated in a counter-clockwise direction so as to break contact with stationary contact 92 only preventive coils .81and 31 will be in series circuit relation with the two sections 14 and 15 of the transformer winding and if these windings are on a common core as shown in Figs; 1 and 2 they will inductively oppose eachother and thus reduce the reactive impedance drop therethrough to a minimum. If it is desired to further reduce the impedance drop through the preventive coils auxiliary stationary contacts such as disclosed in Fig.- 2 may be added to Fig. 3. In Figs. 1, 2 and 3, the stop members 29 are for the purpose of limiting the rotational movement of the respective movable contacts.

It will be apparent to those skilled in the art that the design of the preventive coils with respect to heating will be influenced by the manner in which the switch mechanism is operated. For example, if it is desired to obtain voltage variation in steps which vary by one-half of the voltage between taps by leaving the movable contact member in the bridging positions as well as the other positions, it is essential that the preventive coils be designed for continuous duty, whereas if only tap voltages are desired it is preferable that the switch mechanism be operated so as to only momentarily bridge the adjacent contacts in which event the preventive coils need only to be designed for momentary duty.

Although it is desirable that one of the windings of the transformer 10 be divided into a tapped section and an untapped section as illustrated in Figs. 1 and .2, or into two tapped sections as in Fig. 3, in order that the induced voltage between the inactive end of each tapped winding section and other portions of the winding or the core may be kept within limits to thereby effect a saving in the insulation of the windings, it is to be understood that the present invention is applicable to installations in which the untapped sections of winding, 'such as 15 in Figs. 1 and 2, are omitted, and is also applicable to tapped autotransformers having a single winding.

It is to be understood that the matter herein disclosed is merely illustrative of the invention and is not to be taken in a limiting sense, changes in details of construction and arrangement of parts being permissible so long as within the spirit of the invention and the .scope of the claims which follow.

It is claimed and desired to secure by Letters Patent:

1. In a tap changing system, the combination of a winding having a plurality of taps, a'tap changing switch having a plurality of stationary contacts and a movable contact device operable to selectively engage said stationary contacts, and a plurality of preventive coils each serially connected between one of said taps and one of said stationary contacts, the preventive coils associated with adjacent taps being arranged in inductive opposition.

2. In a tap changing system, the combination of a winding having a plurality of taps, a tap changing switch having a plurality of stationary contacts and a movable contact device operable to selectively engage said stationary contacts and to bridge adjacent stationary contacts when moving from one contact to another, and means connecting said taps to the respective stationary contacts, said means comprising a plurality of preventive coils each arranged in inductive opposition with respect to the preventive coils connected with adjacent taps.

3. In a tap changing system, the combination of a winding having a plurality of taps, a plurality of preventive coils each having one end thereof connected to one of said taps, each preventive coil being arranged in inductive opposition with respect to the preventive coils connected to adjacent taps, and switching means for-"selectively completing circuits through various portions of said winding and through certain of said preventive coils.

4. In a tap changing system, the combination of a line, a winding having a plurality of taps,

a plurality of preventive coils each having one end thereof connected to one of said taps, each preventive coil being arranged in inductive opposition to the preventive coils connected to adjacent taps when current flows through said winding and through preventive coils connected to adjacent taps, and switch mechanism operable to connect portions of said winding across said line selectively through one or more of said preventive coils.

5. In a tap changing system, the combination of a winding having a plurality of taps, switch mechanism having a plurality of contacts, separate preventive coils connected between each of said taps and a corresponding contact of said plurality of contacts, said switch mechanism being operable to selectively complete circuits through portions of said winding and through certain of said preventive coils so that said certain coils inductively oppose each other.

6. In a tap changing system, the combination of a winding having a plurality of taps,- switch mechanism having stationary contacts equal in number to said taps, a preventive coil serially connected between each tap and corresponding stationary contacts, and a core member independent of said winding, each alternate preventive coil being wound on said core member in the opposite direction with respect to the other of said preventive coils, said switch mechanism including means operable to selectively and progressively engage said stationary contacts so that adjacent contacts are bridged between each engagement of a stationary contact.

7. In a tap changing system, the combination of a winding having a plurality of taps, switch mechanism having a plurality of contacts, a preventive coil serially connected between each of said taps and a corresponding contact of said switch mechanism, said switch mechanism being operative to selectively complete one or more circuits through portions of said winding and through certain of said preventive coils so that said certain coils inductively oppose each other, said switch mechanism comprising means for short circuiting said preventive coils when a single circuit is completed through said winding.

8. In a tap changing system, the combination of a winding having a plurality of taps, a tap changing switch having a plurality of stationary contacts and a movable contact device operable to selectively engage said stationary contacts, and a plurality of preventive coils each serially connected between one of said taps and one of said stationary contacts, the preventive coils associated with adjacent taps being arranged in inductive opposition, said switch comprising means for short circuiting the preventive coil associated with the selected stationary contact.

9. In a tap changing system, the combination of a line, a winding having a plurality of taps, a plurality of preventive coils each having one end thereof connected to one of said taps, each preventive coil being arranged in inductive opposition to the preventive coils connected to adjacent taps when current flows through said winding and through preventive coils connected to adjacent taps, and switch mechanism operable in certain positions thereof to selectively connect various portions of said winding across said line through two of said inductively opposed preventive coils and operable in other positions to connect various portions of said winding directly across said line.

10. In a tap changing system, the combination of a Winding comprising two independent sections each having a plurality of taps, a plurality of preventive coils each having one end thereof connected to one said taps respectively, the preventive coils connected with adjacent of said taps being arranged in inductive opposition, and switching means for selectively connecting portions of said sections in series through certain of said preventive coils.

11. In a tap changing system, the combination of a winding comprising two independent sections each having a plurality of taps, two groups of preventive coils, independent magnetic cores for said groups of preventive coils, each of said preventive coils being connected with the respective taps of said sections in inductive opposition with respect to the preventive coils of the same group connected to adjacent taps and switch mechanism for selectively connecting various portions of each of said sections in series circuit relation through certain of said preventive coils.

WILLIAM C. SEALEY. 

